1: KISS

Keep it simple, stupid ! Don't complex your code for a small enhancement and keep in mind that small and comprehensive code is easyer to maintain in the future.

2: DRY

DRY stands for Don’t Repeat Yourself. This principle should help you to avoid code duplication or in other words, if you have to copy-past your code for the same function, you break this rule.

3: Single Responsibility

Your class should have a single responsibility and only one reason to change. Don't mix methods in the same class but create a new class with a method that could me reuse in other classes.

4: Document your code

It's simply a coding standard that you have to respect. Your own code should already explain what it do just by reading your variable, function and class names.

5: Refactor

Restructure your code without changing its external behavior. You will increase your "bad code" to a much better code.